In modern network computer systems, the ever increasing need for data storage space often exceeds the amount of storage initially planned for by designers of the system. One method of meeting the need for added data storage space in systems employing RAID (Redundant Array of Independent Disks) architectures is to provide additional storage devices or hard drives to the system. The addition of new hard drives to existing RAID volumes (logical drives) has the added advantage of providing additional spindles, which in turn increases performance of the data storage system significantly.
To take advantage of a new disk in a RAID volume, the user must migrate (or reconstruct) the new disk using the existing volume (logical drive). However, most RAID systems are deployed in mission critical systems that involve significant cost for shutting down for migration. If power fails while data is migrating the stored data may be corrupted. This problem is efficiently mitigated by hardware based RAID systems, since such systems can keep track of the last block been migrated by using non-volatile memory such as NVRAM (Non-Volatile Random Access Memory), or the like.
In storage systems employing software based RAID with IDE Drives (Parallel & Serial ATA) or SCSI drives, where the driver has no access to private non-volatile memory, safe online migration is more difficult. In the absence of any persistence storage for storing the migration pointer in the event of power failure across system boots, the software/driver runs risk of data corruption. One solution to this problem is to store the migration pointer after every block of migration on a reserved sector in the disk. However, this solution generates an extra write and seek to the reserved sector for every block migrated and, thus, involves a significant performance penalty.
Consequently, it would be desirable to provide a method for providing online raid migration without non-volatile memory. The system and method should protect online migration of data from a failure event such as a power failure, or the like with negligible performance loss. In this manner, data can be recovered if power fails while migration is in progress, and migration resumed without the use of non-volatile memory.